Lithos 202–203 (2014) 283–299

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Lithos

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Subcontinental rift initiation and ocean-continent transitional setting of the Dinarides and Vardar zone: Evidence from the Krivaja–Konjuh Massif, Bosnia and Herzegovina

Ulrich H. Faul a,⁎, Gordana Garapić b,3,Boško Lugović c,1,2 a Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA b Department of Earth Science, University of California, Santa Barbara, Santa Barbara, CA, USA c Department of Mineralogy, Petrology and Mineral Resources, University of Zagreb, Zagreb, Croatia article info abstract

Article history: The Dinaride and Vardar zone ophiolite belts extend from the south-eastern margins of the Alps to the Albanian Received 21 February 2014 and Greek ophiolites. Detailed sampling of the Krivaja–Konjuh massif, one of the largest massifs in the Dinaride Accepted 24 May 2014 belt, reveals fertile compositions and an extensive record of deformation at spinel peridotite facies conditions. Available online 4 June 2014 High Na2O clinopyroxene and spinel–orthopyroxene symplectites after garnet indicate a relatively high pressure, subcontinental origin of the southern and western part of Krivaja, similar to orogenic massifs such as Lherz, Keywords: Ronda and the Eastern Central Alpine peridotites. Clinopyroxene and spinel compositions from Konjuh show Balkan ophiolites Subcontinental lithosphere similarities with fertile abyssal peridotite. In the central parts of the massif the spinel lherzolites contain locally Rift initiation abundant patches of plagioclase, indicating impregnation by melt. The migrating melt was orthopyroxene under- Ocean continent transition saturated, locally converting the peridotites to massive olivine-rich troctolites. Massive gabbros and more Melt migration evolved gabbro veins cross-cutting peridotites indicate continued melt production at depth. Overall we infer Deformation that the massif represents the onset of rifting and early stages of formation of a new ocean basin. In the south of Krivaja very localized chromitite occurrences indicate that much more depleted melts with supra- subduction affinity traversed the massif that have no genetic relationship with the peridotites. This indicates that volcanics with supra-subduction affinity at the margins of the Krivaja–Konjuh massif record separate processes during closure of the ocean basin. Comparison with published compositional data from other Balkan massifs shows that the range of compositions within the Krivaja–Konjuh massif is similar to the compositional range of the western massifs of the Dinarides. The compositions of the Balkan massifs show a west to east gradient, ranging from subcontinental on the western side of the Dinarides to depleted mid-ocean ridge/arc compositions in the Vardar zone in the east. This is consistent with the hypothesis that both ophiolite belts originate in a single ocean, rather than from two separate basins. A distinct decrease in fertility occurs in the south of the Dinarides towards the Albanian ophiolites with supra-subduction affinity. © 2014 Elsevier B.V. All rights reserved.

1. Introduction 2006; Robertson et al., 2009,seeSection 6 for further discussion of the tectonic units) to the east provide the link between the Alpine peridotites The Dinaride ophiolite belt together with the peridotites of the Vardar to the north-west and the Albanian and Greek peridotites (Hellenides, Zone Western Belt are part of the Alpine–Himalayan suture zone of the e.g. Smith, 1993) to the south (Fig. 1). former (Neo-)Tethys ocean that separated Gondwana and Eurasia during The Krivaja–Konjuh massif in central Bosnia is one of the largest the Mesozoic (e.g. Dilek and Furnes, 2011; Hrvatović and Pamić,2005; complexes within the Dinaride ophiolite belt with an area of Karamata, 2006; Pamić et al., 2002; Robertson et al., 2009, and references ~650km2 (Fig. 2, Pamić et al., 2002; Bazylev et al., 2009). For compari- therein). These two belts, together with the Main Vardar Belt (Karamata, son, the Ronda massif in southern Spain has an area of about 300 km2 (Soustelle et al., 2009). The massif itself is considered to consist of two ⁎ Corresponding author at: Dept. of Earth, Atmospheric and Planetary Sciences, 54-714, parts, separated by a major northwest–southeast trending fault. This Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139- fault is inferred to juxtapose a more fertile western part (Krivaja) and 4307. a more depleted eastern part (Konjuh). Different inferences exist for E-mail address: [email protected] (U.H. Faul). 1 Formerly at. the tectonic setting of the massif as a whole, and whether the two 2 Deceased 12 May 2013. parts originate in different settings. Based on the geochemistry of a 3 Now at: Department of Geological Sciences, SUNY New Paltz, NY, USA. few samples, the relatively fertile peridotites from the Krivaja have

Fig. 1. Overview of the Balkan peridotite massifs (after Lugović et al., 1991; Ustaszewski et al., 2010). Dinarides: Ko, Kozara; LC, Ljubić–Čavka; BO, Bosanski Ozren; Bo, Borja; KK, Krivaja– Konjuh; Zl, Zlatibor; Bi, Bistrica; SO, Sjenički Ozren; Tu, Tuzinje. textitVardar Zone: Ma, Maljen; To, Troglav; St, Stolovi (Ibar); Ta, Trnava; Ba, Banjska. Albanide–Hellenides: Mi, Mirdita; Br, Brezovica. S P: Skutari-Peć line. Colors correspond to compositions in Fig. 10, indicating west to east depletion. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) been associated with either subcontinental lithosphere or a mid-ocean range of ages (see e.g. Pamić et al., 2002; Robertson et al., 2009,andref- ridge setting (Bazylev et al., 2009; Lugović et al., 1991; Robertson erences therein for more details). The massif is surrounded by smaller et al., 2009), but a back-arc basin setting has also been inferred for the ultramafic bodies, with the nearest larger one about 20 km to the Konjuh (Lugović et al., 2006; Pamić et al., 2002, and references therein). north (Fig. 1, Bosanski Ozren, with an area of ~300 km2). Volcanics found at the margins of the massif as well as in the ophiolitic The massif is partially bordered by Triassic and Jurassic limestone. mélange nearby that have arc/back-arc signatures complicate the inter- We examined the contact between peridotite and Triassic limestone pretation (Lugović et al., 2006; Robertson et al., 2009). in a limestone quarry in the north-western corner of the massif The field observations and analyses described in this manuscript are (Fig. 2). This contact showed only minor calcite veins extending from predominantly from Krivaja, although some samples were also collect- the limestone into the overlying completely serpentinized peridotite, ed from Konjuh (Fig. 2). The field observations indicate that the perido- indicating relatively low temperatures on contact between the two tites were exhumed in a magma-poor ocean floor setting, while units. microstructural observations and mineral chemistry indicate a fertile, Parts of the southern margin of the Krivaja are bounded by a meta- subcontinental origin, consistent with inferences from the fertile nature morphic sole, grading from greenschist-facies in its lowermost parts to of many of the Dinaride massifs (Bazylev et al., 2009; Lugović et al., amphibolite–granulite-facies towards the contact with the peridotites 1991). The compositions of some of the south-eastern parts of the (Pamić et al., 2002). The pressure estimates range up to 1 GPa at tem- Krivaja and from parts of the Konjuh are somewhat more depleted, peratures between 620 and 830 °C (Operta et al., 2003). The contact be- with mid-ocean ridge (MOR) affinity. Despite the near complete ab- tween metamorphic sole and ophiolitic mélange is described as of sence of harzburgites and dunites, the massif contains an extensive re- tectonic origin (Operta et al., 2003). Ages obtained by K–Ar dating of cord of melt migration that culminates in olivine-rich troctolites. amphibolites range from 157 to 170 Ma (Pamić et al., 2002), although These will be described in more detail separately. aSm–Nd isochron from peridotites from three different massifs suggests a younger age of 136 Myr (Lugović et al., 1991). 2. Geologic setting The division into separate sections (Krivaja in the west and Konjuh in the east) is in part based on the occurrence of a major fault zone The Krivaja–Konjuh peridotite massif is embedded in an ophiolitic that can be traced from the northwest to the southeast through the mélange with a matrix of fine-grained sedimentary origin. The mélange massif. We examined the fault zone in three areas (Džinica, Dištica contains fragments of ultramafic, mafic intrusive and volcanic rocks, as and Vojnica, Fig. 2). The fault zone and adjacent rocks are completely well as limestones and cherts (indicating a deep water origin) with a serpentinized, blocky at Dištica and reduced to a microbreccia in Vojnica U.H. Faul et al. / Lithos 202–203 (2014) 283–299 285

Fig. 2. Simpliﬁed geological map of the Krivaja–Konjuh massif with sample locations indicated. The map was constructed from four sheets of geologic maps of the former Yugoslavia (Zavidovići, Tuzla, Vlasenica, Vareš, Federal Geological Institute, 1971–1990). Sample locations marked in red represent spinel peridotites, orange transitional, blue are plagioclase peridotites (see text). Major faults are represented by dashed lines, the location of pictures shown in Fig. 3 are shown by green dots. Not all faults are shown. The fault separating the Krivaja portion to the west from the Konjuh portion to the east is indicated. The extent of gabbro and troctolite outcrops are approximate, both tend to occur together and are interlayered with peridotite at the margins. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)

(Fig. 3a) and Džinica. In all locations the fault rocks appear to be of man- high erosion rates; they are associated with faults and shear deforma- tle origin, with no indications of intercalated crustal lithologies. Similar tion structures rather than inﬂation (expansion) structures. Carbonate relatively well developed serpentinized shear zones also occur else- veins in a joint patterns have also not been observed in weathered where in the massif (Fig. 3b). outcrops away from stream beds. Based on the structural observations In some cases fault zones within the massif and near the main we therefore infer that the ophicalcites in this massif are not due to re- Krivaja–Konjuh fault are associated with ophicalcites (Fig. 3d), where cent surface carbonation reactions. limestone is in conformable contact with and contains brecciated fragments of serpentine or gabbro. The breccias do not include sandstone 3. Peridotites and show no evidence of prior transport of clasts, in contrast for example to observation from Lherz (Lagabrielle and Bodinier, 2008). Boulders 3.1. Overview from watercourses that are entirely within the massif similarly show conformable contacts between peridotite and limestone or chert Samples were collected from all parts of Krivaja, as well as four loca- (Fig. 3c). A deep water origin is also indicated by minor pillow basalts tions from Konjuh (see Fig. 2 and Table 1 for place names and locations). and cherts observed in the central-western part, although the structural The freshest samples were typically found along stream beds, which relationship of these outcrops with the surrounding peridotites is not also provided relatively convenient access. The choice of samples for easy to ascertain. analysis was based on coverage of the massif as well as freshness. The surface carbonation reactions described by Kelemen and Matter Whenever possible samples from outcrop were chosen for analysis, (2008) in a desert environment with low erosion rates produce sets of but in some cases boulders collected in stream beds (from relatively expansion joints, as shown in their Fig. 1. In contrast, the carbonates small tributary streams wholly within the massif) were fresher. All sam- and ophicalcites in the Krivaja are found in incised stream beds with ples were affected by serpentinization, introducing uncertainties in 286 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

c d

Fig. 3. Examples of faults and shear zones from Krivaja–Konjuh. (a) Outcrop of the Krivaja–Konjuh fault at Vojnica. The shear zone material consists of microbrecciated serpentine. Adjacent rocks are also completely serpentinized. Field examination suggests that the serpentinized rocks in the shear zone are of mantle origin, rather than amelange,ormaﬁc rocks. (b) Outcrop of a serpentinized fault at Kozjak. (c) Limestone and chert layers atop serpentinized peridotite at Romanovac. (d) Limestone containing serpentinite fragments adjacent to serpentinite breccia in an outcrop in Dištica. The larger fragments in the breccia consist of serpentinized peridotite. The outcrop is located near the Krivaja–Konjuh fault and at the border between peridotite and amphibolite.

analysis, point counting of modes and grain size determination from the most evolved, with near pegmatitic domains (Fig. 4c). Thin, cross thin sections. Grain sizes and deformation intensity vary locally, the cutting gabbro veins as well as thicker anastomosing veins occur occa- grain sizes given below are intended to be representative for a given sionally in all parts of the massif where plagioclase is observed. locality. Particularly the rocks in faults and shear zones are almost al- Locally abundant gabbro veins as well as outcrop-scale variable ways completely serpentinized and in some instances further altered proportions of plagioclase patches and veinlets occur in Stara Kamenica to talc and clay, making identification of the original lithology difficult (Ska1, 5). The very heterogeneous lithologies range from dunitic in the field. An overview over the samples analyzed is given in patches, to harzburgitic to essentially gabbroic compositions (Fig. 4e). Table 1, the sample locations are shown in Fig. 2. Variable lithologies including small (10–20 cm sized) dunite patches The Krivaja–Konjuh massif consists of spinel and plagioclase perido- also occur in Kozjak (Koz9), Sadjevica (Sad14) and in Maoča(Konjuh). tites as well as massive troctolites and gabbros. The peridotites consist Clinopyroxene-rich pyroxenite patches, veins and layers occur of lherzolites with clinopyroxene (cpx) contents from just above 5% in Sadjevica. The pyroxenites are parallel to the foliation, which is ranging up to 15%. Rocks that can be classified as dunite or harzburgite expressed by the alignment of somewhat elongate orthopyroxene based on mineral mode are volumetrically very minor and typically con- (opx) grains (Fig. 4b). In one location pyroxenite veins appear to be tain one or a combination of cpx, plagioclase and spinel with interstitial gently folded and somewhat boudinaged. Relatively thin pyroxenite geometries. The sparsity of dunites in the Krivaja–Konjuh massif is sim- veins/layers occur throughout the massif (e.g. Dištica, Vojnica, ilar to their near complete absence in the Dinarides overall (Lugović Duboštica, Tribija, Maoča). In Vojnica and similarly in Muška Voda in et al., 1991). Konjuh more opx-rich layers occur at a small angle to the foliation. Spinel and plagioclase lherzolites occur both in Krivaja and Konjuh. Chromite mines have been mapped in the south of the Krivaja by the The western and southern parts of Krivaja, bounded to the north and Federal Geological Institute of Yugoslavia (Federal Geological Institute, east by the massive troctolites, consist of spinel peridotites (Fig. 2). 1971 –1990). The largest mine site near Duboštica is accessible and In Konjuh spinel peridotites are found in the north-eastern part contains abundant chromitite fragments in the vicinity of the mine en- (Zlaća). The spinel peridotites show no signs of re-equilibration in trance. The peridotites immediately surrounding the mine are heavily the plagioclase stability field. Plagioclase peridotites occur to the serpentinized, however. Outcrop of peridotite at a distance of about north and east of the troctolites in Krivaja, and the center and 150 m from the mine entrance, while still partially altered is very fertile south of Konjuh. (see below), spinel rich (N3%) spinel peridotite, and typically highly The lithologies in the central-western portion of the Krivaja shown deformed. as troctolites and gabbros in Fig. 2 range from massive olivine-rich troctolites to troctolites, olivine gabbros and gabbros. The adjacent 3.2. Microstructures peridotites are intruded by gabbro veins and dikes ranging from mm to m scale (Fig. 4a–c), with diffuse (relatively high temperature) to The peridotites throughout the massif record a high grade of sharp sided (lower temperature) contacts with the host rock. Cross- deformation and associated recrystallization. The deformation grade of cutting relationships between the gabbro veins indicate at least three the spinel peridotites in Krivaja is on average higher than in Konjuh. generations in some locations, with the latest generation appearing The largest remaining porphyroclasts of olivine and orthopyroxene U.H. Faul et al. / Lithos 202–203 (2014) 283–299 287

Table 1 Sample locationsa, outcrop and thin section notes.

Sample Location T, opx °Cc Notes number

Krivaja Limestone quarry Contact between Triassic limestone and peridotite (serp.) Ska1 St. Kamenica PL; anastomosing veins of coarse ol gab., ol fg, euhedral, plag interstitial, up to 5% magnetite. Ska5 St. Kamenica Multiple episodes of melt migration: PL, fg; plag dunite/troct. very fg; sp; plag interstitial. Ska16 St. Kamenica Trans.; mg porph., part. mosaic, plag patches (interstitial)//ol elongation, dismembered ol Ul4 Ulen PL; opx porph., elongate, foliated; ol recrystallized more fine-grained; little spinel Cau1 Čauševac 1180 Trans.; large lobate ol w. subgrain bd, ol matrix mosaic texture; plag interstitial, undeformed; dark brown sp Cau2 Čauševac Boulder w. PL — gabbro contact, PL layered w. coarse and fine ol, coarse opx, porph. brown sp. mantled with plag Koz9 Kozjak Contact troct.-PL. PL has coarse, el. porph. + fg. ol; opx: corroded gb, exsolved cpx, ol; plag interstitial; troct.: plag trails, minor elongate opx Koz13 Kozjak Shear zone, gabbro peridotite Luz17 Lužnica 960 SL; mg porph.; coarse, dark brown sp + fine light brown sp Taj5 Tajašnica SL; cg porph., elongate ol (sgb), + fg matrix; sp-opx intergrowths (rounded); fg. sp Saj5 Sajavica 1060 PL, all ol fg; opx and cpx porph., ol included in opx; dark brown sp rimmed w. plag + opx. Sad14 Sadjevica PL; mg. porph., dunite patch Sad26 Sadjevica 1080 PL, mg.; ol porph. + fg matrix; plag patches; no sp Dzi11 Džinica 1010 PL, ol mg. mosaic, few porph.; plag patches; sp rimmed w. plag + opx (undeformed). Dis9 Dištica Contact amphibolite–peridotite; limestone Dis11 Dištica KK fault, serpentinized, blocky Rom1 Romanovac Ophicalcite. Rom3 Romanovac SL; mg; thin gabbro veins; sp light brown fg. Voj3 Vojnica KK fault, serpentinized, granular. Voj4 Vojnica Trans.; mylonitic, coarse spinel rimmed by plag. Voj8 Vojnica SL; mylonitic, some elongate opx (20:1),N1cm. Dub2 Duboštica SL; ol largest porph., undulose extinction; opx porph. elong. corroded gb.; sp light brown, fg, opx intergrowth. DubCr3 Duboštica 890 SL; (ultra-) mylonitic, fine spinel trails. ~350 m from chromite mine/chromitites. DbC2 Duboštica Chromitite from main chromite mine with attached silicates containing fresh cpx. Massive sp dark brown. d18b Duboštica Chromitite from chromite mine Sla3 Slani Potok SL; light brown sp trails//elongate ol proph. Tri1 Tribija SL; porph.; ol mg elongate, ol included in opx. Tri6a Tribija SL; layered peridotite–pyroxenite. Deformd, per. more fg some larger opx porph in per.; light brown elongate sp.

Konjuh MVS1b Muška Voda PL; mg. KPer6a R. Krivaja PL; mg porph, interstitial. plag. Mao3b Maoča SL, Trans.; dark brown sp, interstitial. plag. Zla3b Zlaća SL; cg–mg porph.

Abbreviations. PL, SL: plagioclase, spinel lherzolite; Trans.: Transitional PL–SL; ol: olivine; sp: spinel; plag: pladioclase; fg, mg, cg: fine, medium, coarse grained; mosaic indicates recovery/ grain growth after deformation; porph.: porphyroclastic; troct.: olivine troctolite consisting of 80–90% olivine, plagioclase and sometimes minor opx, cpx, spinel; sgb: subgrain boundaries. a See Fig. 2,andTable 3 for GPS coordinates. b Analyses from Šegvić (2010). c Temperature estimates based on the Ca-in-opx thermometer of Brey and Köhler (1990) (thin section averages). range in size from 3 to 5 mm, suggesting that this may have been the of the coarse symplectites resulted in vermicular spinel grains intersti- grain size before deformation of the peridotite (Fig. 5a). Olivine is tial to opx neoblasts (Fig. 5c). No symplectites remain in mylonites frequently recrystallized, occasionally to grain sizes b100 μm(Fig. 5b). and ultramylonites (Fig. 5b), which contain ribbons of nearly touching, Remaining olivine porphyroclasts are elongate with parallel subgrain fine-grained light brown (interstitial) spinels that extend across indi- walls showing undulose extinction (Fig. 5a, d). Dismembered grains vidual thin sections. The highly deformed spinel peridotites show can be identified by their simultaneous extinction. Based on the degree no signs of recovery and grain growth after deformation, indicating of recrystallization the microstructures can be characterized as ranging that temperatures remained relatively low during exhumation. from protomylonitic (with an olivine mean grain size of ~0.7 mm, Porphyroclastic, dark brown and fine-grained, light brown spinel coex- Duboštica) to mylonitic–ultramylonitic (mean grain size of 0.3 mm, ists in the central-western part (Lužnica) as well as the southern part Vojnica; to 0.1 mm, Sajavica). (Duboštica) of the massif. Coarse, undeformed symplectites of opx and spinel occur in the In the spinel peridotites orthopyroxene frequently occurs as western-most part (Tajašnica, Fig. 5e). Garnet-shaped spinel–opx– porphyroclasts with exsolution lamellae, occasionally showing extreme plagioclase intergrowths also occur in Sajavica (Fig. 5f). Deformation elongation with aspect ratios N10:1 (Taj5, Voj8, Fig. 5b). Locally it is 288 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

Fig. 4. Outcrop-scale features representing melt migration. (a) Anastomosing gabbro veins surrounding blocks of peridotite (Stara Kamenica). (b) Olivine-gabbro vein cross-cutting foliation in peridotite. The foliation is marked byopx porphyroclasts, with foliation-parallel pyroxenite layers and lenses (Sadjevica). (c) Intrusion of three generations of gabbro veins into plagioclase peridotite near the contact with massive gabbro units. The gabbro compositions range from olivine-rich to evolved-pegmatitic (Stara Kamenica). (d) Peridotite strongly modiﬁed by migrating melts. The darkest brown colors indicate plagioclase–dunite compositions, lighter brown are remnants of the original lherzolite, more plagioclase-rich portions are white. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)

alsocompletely recrystallized to fine grain sizes, giving the rock a data were corrected for matrix effects with the CITZAF program smooth appearance on weathered surfaces. Clinopyroxene ranges (Armstrong, 1995). Additional microprobe analyses were performed from porphyroclastic (particularly the spinel peridotites in Zlaća, also at the Research School of Earth Sciences, Australian National University, Vojnica) to completely recrystallized (e.g. the spinel peridotites in using a Cameca SX-100 electron microprobe operating at 15 kV and a Duboštica). beam current of 20 nA. Standards were analyzed before and during By contrast microstructures in the plagioclase peridotites show each session with 1-sigma standard deviations b0.5%. The same analyt- onset of recovery after deformation. Olivine is on average relatively ical protocol was used for all minerals on each probe. Typically one fine-grained (e.g. 0.6 mm, Čauševac), but the size difference between thin section was analyzed from each locality for all the phases present. large and small grains is not as pronounced as in the spinel peridotites. Except for Ca contents in opx for the thermometer of Brey and Köhler Elongate porphyroclasts with subgrain boundaries still occur, but they (1990) the compositions were not averaged. Plagioclase is commonly have largely smooth grain boundaries (Fig. 6a, b). Smaller grains tend altered, and is not reported here. Compositional ranges are shown in to have more euhedral shapes, indicating grain growth after defor- Table 2, the complete dataset is included as supplementary material. mation. Plagioclase in these rocks occurs as interstitial patches or ribbons (Fig. 6c), which are aligned parallel to the foliation where 4.2. Mineral chemistry it is observable. Plagioclase also occurs as reaction rims around spinel (e.g. Fig. 6b). Significantly, plagioclase, whether in the form of 4.2.1. Olivine overgrowths around spinel or interstitial patches shows no sign of Overall the compositions of the peridotites are moderately depleted deformation. Similarly opx porphyroclasts, in the process of being relative to MORB source mantle (e.g. DMM, Workman and Hart , 2005). replaced by cpx and olivine (Fig. 6d) show no signs of deformation. This is expressed by an average olivine Mg# of 90.2 with a range be- Cpx in the plagioclase peridotites occurs as porphyroclasts or grains tween 89.3 and 91.1 for Krivaja (c.f. DMM 89.5, see supplementary with interstitial shapes but with an overall lower mode compared to Table). Although each location shows some variability, peridotites spinel peridotites. from the southeast in Krivaja tend to be at the depleted end with the highest Mg# (e.g. Tribija, Vojnica), while the plagioclase peridotites 4. Compositions from the northern part tend to have the lowest Mg# (e.g. Sajavica). Olivines from Konjuh show the same narrow range in Mg#, with an av- 4.1. Analytical procedures erage near Mg# 90 (Šegvić, 2010). Interstitial olivine in the chromitites has significantly higher Mg# than all other rocks, from 91.6 to above Microprobe analyses were performed at the MIT Electron Micro- 92.2 (Šegvić,2010). probe Facility on both the JEOL-JXA-8200 and JEOL-JXA-733 with 15 kV acceleration potential and a beam current of 10 nA and a beam 4.2.2. Orthopyroxene diameter of ~1 μm. Counting times were 20–40 s per element, resulting Large, porphyroclastic opx grains commonly show exsolution in counting precisions of 0.5–1.0% 1-sigma standard deviations. The raw lamellae and internal deformation features in the spinel peridotites U.H. Faul et al. / Lithos 202–203 (2014) 283–299 289

a b

c d

e f

Fig. 5. Spinel peridotite microstructures. (a) Spinel lherzolite near Duboštica showing the largest remaining olivine porphyroclasts in Krivaja, characterized by undulose extinction (Dub2). (b) Mylonitic microstructure with elongate opx porphyroclasts. Olivine is completely recrystallized (Voj8). (c) Incipient recrystallization of coarse opx-spinel symplectite and an opx porphyroclast. The inset shows that the recrystallized parts of the coarse spinel become interstitial to opx neoblasts (Dub2). (d) Elongate and partially dismembered olivine grains. Opx is recrystallized in this sample (Taj5). (e) Coarse intergrowth of spinel and orthopyroxene, suggesting a garnet origin (Tajašnica, Piccardo et al., 2007). (f) Spinel, plagioclase and orthopyroxene in the shape of a garnet crystal in Sajavica. Fluid inclusions are also present. The pseudomorph is surrounded by an alteration rim. While the olivine grain size is reduced to 0.1 mm in this area, the spinel intergrowths appear undeformed.

(Fig. 5b, c). In the transitional and plagioclase peridotites, besides inter- whole the most obvious feature is the difference in composition be- nal deformation, opx porphyroclasts also show signs of reaction with tween plagioclase-bearing and plagioclase-free peridotites with regard other phases (Fig. 6c, d). Correspondingly, the compositions show a to their Na2O and Al2O3 contents (Fig. 7) (Supplementary Table). As a wide range within individual grains and thin sections (Supplementary function of TiO2 the spinel peridotites form a trend at Al2O3 contents be- table) and are not further discussed here. Particularly in the transitional tween ~5 and 7 wt.% towards the model MORB source composition peridotites large opx grains tend not to be in equilibrium with frequent- DMM (Workman and Hart, 2005) at the fertile end (Fig. 7a). Plagioclase ly smaller cpx grains, so that two-pyroxene thermometry does not yield peridotites form a similar trend but at lower Al2O3 contents due to the useful temperature estimates. Thin section averages of CaO in opx were partitioning into plagioclase (Dick et al., 2010; Rampone et al., 1993). used for temperature estimates for individual localities with the Brey Peridotites from Čauševac, Stara Kamenica, and Maoča contain cpx and Köhler (1990) thermometer. grains with both high and low Al2O3 contents, straddling the two trends. The Na2O contents of cpx from the Krivaja spinel peridotites range 4.2.3. Clinopyroxene to twice the value for DMM, and are consistently higher than those of With some scatter, cpx compositions from individual localities have the plagioclase-bearing peridotites (Fig. 7b). Overall the clinopyroxenes distinct characteristics (see supplementary table). For the massif as a form a trend of moderately decreasing Al2O3 contents for a broad range 290 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

a b

c d

Fig. 6. Plagioclase peridotite microstructures. (a) Peridotite with interstitial and euhedral plagioclase grains. In comparison to the spinel peridotites the grain size is relatively uniform with no indication of deformation also in the plagioclase (Koz9). (b) Microstructure showing recovery from deformation. A previous high grade of deformation is evident in elongate and partially dismembered olivine grains, similar to the elongate grains in spinel peridotites (Fig. 5d). Black elongate patches in the center and top of the image are spinel grains surrounded by a rim of plagioclase grains. Interstitial plagioclase patches are also indicated. Opx grains are being replaced by olivine and cpx (Cau2). (c) Plane-polarized light image of ribbons and patches of (altered) plagioclase. The porphyroclastic orthopyroxene grain at the top of the image is partially replaced by clinopyroxene and olivine (Koz9). (d) Cross- polarized image of an opx grain that is being replaced by olivine and cpx (Koz9).

of Na2O. With few exceptions, rocks from Konjuh form a steeper trend in Al2O3 and TiO2 than in any other rocks from the massif, but they do starting from Al2O3 contents as high as Krivaja, but at Na2O below 1%. have somewhat elevated Na2O contents. The highest Al2O3 and Na2O contents in Fig. 7 come from a pyroxenite vein in sample Tri6a. Cpx compositions outside of the vein in the same 4.2.4. Spinel thin section are similar to other spinel peridotites. Cpx compositions Spinel compositions from Krivaja–Konjuh peridotites form the in the chromitites from Duboštica are signiﬁcantly more depleted same groupings as cpx compositions (Fig. 8). Spinel peridotites from

Table 2 Compositional ranges, wt.%.

Oxide wt.% SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO NiO Na2O Plag. P Ol 39.6–41.3 ––– 9.5–10.3 0.11–0.19 48.8–51.0 – 0.31–0.48 Opx 53.7–56.7 0.06–0.26 1.8–7.3 0.35–0.91 5.5–7.2 0.09–0.20 29.0–34.9 0.36–3.68 – Cpx 49.8–53.7 0.16–0.87 1.88–3.77 0.55–1.52 2.29–3.43 0.0–0.19 16.0–18.6 20.2–24.8 – 0.09–0.57 Sp – 0.01–0.85 20.7–56.5 9.8–41.9 12.8–28.3 0.06–0.83 8.0–20.2 0–0.36

Transitional Ol 39.6–41.3 ––– 8.8–10.1 0.03–0.21 49.3–51.2 – 0.33–0.44 Opx 54.4–55.9 0.09–0.13 2.67–4.33 0.74–1.00 6.3–6.7 0.13–0.20 32.5–33.9 1.27–2.1 – Cpx 48.7–53.7 0.22–0.62 2.45–7.85 0.28–1.41 2.21–3.08 0.01–0.16 14.4–18.0 21.8–23.6 – 0.24–1.38 Sp – 0.01–1.07 28.7–59.0 6.9–36.4 11.6–22.6 0.01–0.29 11.9–19.5 0.0–0.17

Spinel P Ol 39.2–41.4 ––– 8.8–12.7 0.01–0.22 45.7–50.5 – 0.32–0.48 Opx 53.6–57.1 0.05–0.18 2.89–6.44 0.04–0.57 6.20–8.19 0.14–0.30 31.7–33.68 0.31–1.07 – Cpx 50.1–54.8 0.16–0.61 2.46–8.89 0.05–1.31 2.11–4.94 0–0.18 13.5–18.4 17.5–23.7 – 0.42–2.62 Sp – 0.01–0.11 48.8–62.5 7.3–19.1 10.8–14.4 0.0–0.31 17.9–20.1 – 0.0–0.44

Chromitite Cpx 49.7–54.2 0.06–0.30 1.22–4.51 0.51–1.15 1.13–2.71 0.0–0.12 16.4–17.4 22.6–24.0 – 0.17–0.78 Sp – 0.0–0.43 10.4–40.4 23.0–56.5 19.2–24.9 0.0–0.14 9.1–14.9 – 0.25–0.34 U.H. Faul et al. / Lithos 202–203 (2014) 283–299 291

Table 3 compositions of chromitites from Duboštica in the south-western part of Sample locations. the massif are clearly distinct from the compositions of the rest of the Krivaja massif, with much higher Cr# between 0.7 and 0.8. In contrast, spinel peridotites nearest to the chromitite mine site are among the most fertile in Limest. quarry N44°21′37.5″ E18°09′32.0″ – Ska1 N44°20′30.1″ E18°12′54.5″ the massif with Cr# 0.1 0.15. Ska5 N44°20′24.6″ E18°12′51.2″ Ska16 N44°21′41.9″ E18°14′38.6″ 5. Discussion Ul4 N44°20′2.2″ E18°12′59.0″ Cau1 N44°21′10.4″ E18°19′01.1″ Cau2 N44°21′13.1″ E18°18′15.3″ 5.1. Emplacement and exhumation Koz9 N44°19′46.0″ E18°15′22.8″ Koz13 N44°20′01.4″ E18°15′25.9″ The near absence of contact metamorphism at the margins of Luz17 N44°17′21.7″ E18°16′33.9″ both peridotite and metamorphic sole in contact with limestone Taj5 N44°18′23.0″ E18°13′27.8″ implies that the massif was not far above ambient temperature during Saj5 N44°17′59.4″ E18°17′24.3″ Sad14 N44°18′35.4″ E18°20′09.7″ emplacement in its current location in the mélange. The high tempera- Sad26 N44°17′51.6″ E18°19′31.6″ tures inferred for the metamorphic sole at the contact with the perido- Dzi11 N44°19′39.5″ E18°21′05.1″ tites indicate that obduction of the peridotites onto the metamorphic ′ ″ ′ ″ Dis9 N44°18 24.3 E18°23 00.8 sole predates inclusion into the mélange. High temperature records of Dis11 N44°18′26.2″ E18°23′03.6″ Rom1 N44°15′53.6″ E18°18′47.6″ deformation within the massif are therefore unrelated to tectonic em- Rom3 N44°16′16.2″ E18°18′54.6″ placement of the massif in its current location. Voj3 N44°16′01.3″ E18°24′15.6″ Minor outcrops of chert together with pillow basalt interior to the Voj8 N44°15′42.5″ E18°21′48.8″ massif indicate exposure on the ocean ﬂoor in a deep water environment. ′ ″ ′ ″ Dub2 N44°15 11.1 E18°24 46.2 Exhumation and exposure of the peridotites to the ocean ﬂoor is also sug- DubCr3 N44°14′45.5″ E18°19′13.8″ Chromite mine N44°14′35.2″ E18°19′20.0″ gested by the conformable contact of limestone and chert layers on top of Sla3 N44°13′52.8″ E18°19′02.7″ serpentinites criss-crossed by calcite veins (ophicalcite). Very minor oc- Tri1 N44°13′41.4″ E18°26′20.9″ currence of basalts indicates a magma-poor environment. The extensive- ′ ″ ′ ″ Tri6a N44°13 9.8 E18°25 1.2 ly serpentinized faults and shear zones interior to the massif are similar

Konjuh to faults observed for example at the slow-spreading Mid-Atlantic Ridge near the 15°20′ fracture zone (Schroeder et al., 2007), which ac- KPer6a N44°17′30.8″ E18°25′26.7″ commodated exhumation of the peridotites to the seaﬂoor. Overall Muska Voda N44°14′06.3″ E18°34′09.3″ Maoca N44°18′39.4″ E18°26′16.9″ the exhumation of the massif may be comparable to non-volcanic exhu- Zlaca N44°20′15.5″ E18°31′21.5″ mation of peridotites at slow spreading ridges (e.g. Cannat, 1993;

Parts of this area were affected by the Balkan war, local advice should be sought before Schroeder et al., 2007) or continental margins (e.g. Rampone and visiting. Piccardo, 2000; Müntener et al., 2010), although further detailed examination of the shear zones, as well as the cherts, is needed to constrain both parts have the lowest Cr# (=Cr/Cr + Al), highest Mg# their origin and significance. No signs of prograde metamorphism have 2+ (=Mg/Mg + Fe ), and the lowest TiO2 contents (Supplementary been observed in gabbros or peridotites, indicating that following exhu- Table). Cr# of plagioclase peridotites are significantly higher (0.4–0.6). mation, the massif remained at low pressure. Transitional peridotites have low and high Cr#-spinel in one thin section (e.g. Sajavica), but preserve the gap in compositions. The rocks show a 5.2. Melt infiltration similar gap in Mg# in a broad trend towards the lowest Mg# and highest Cr# of the plagioclase peridotites (Fig. 8b). A particular feature of the tran- The map of the Krivaja–Konjuh massif (Fig. 2) shows that plagioclase sitional and plagioclase peridotites is TiO2 contents that extend to 1%. The and transitional peridotites are wide-spread in both parts of the massif.

Fig. 7. Clinopyroxene compositions from the Krivaja–Konjuh massif (squares, this study and Šegvić , 2010) as well as other massifs, abyssal peridotites and xenoliths for comparison.

(a) Al2O3 vs TiO2 and (b) Al2O3 vs Na2O. Plagioclase-free spinel peridotites are shown in red, plagioclase-bearing peridotites that contain cpx both high and low in Al2O3 in one thin section are orange (transitional samples), and apparently equilibrated plagioclase peridotites in blue. Sample Tri6a that contains pyroxenite veins (layers) is marked by an x; cpx from the veins have the highest Al2O3 and Na2O contents. In (a), plagioclase-free and plagioclase-bearing peridotites form separate trends with transitional samples straddling the two trends. Chromitites as well as fertile spinel lherzolites were collected in Duboštica. In (b) only spinel peridotites from orogenic massifs with subcontinental afﬁnity have Na2O contents exceeding that of DMM

[87]. Relatively fertile abyssal peridotites have Na2O contents near or below DMM. Data sources: eastern-central Alpine massifs (upper/lower Platta, UP/LP; Malenco, Mal; Totalp, Tot), Müntener et al. (2010); continental xenoliths, Witt-Eickschen and O'Neill (2005); spinel peridotites from the Gakkel ridge, Hellebrand et al. (2005); from the Southwest Indian Ridge, Seyler et al. (2003);Mirdita,Morishita et al. (2011);Lherz,Le Roux et al. (2007);Ronda,Obata (1980). (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.) 292 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

As explained in more detail below, microstructural as well as composi- in Fig. 7a). The Eastern Central Alpine peridotites (Müntener et al., tional features of the plagioclase peridotites indicate that they originat- 2010) and those from Ronda epOb80 similarly straddle these two ed by melt impregnation, rather than by subsolidus equilibration or in trends. situ melting. Observations from ODP Leg 153 (MARK area, Niida, 1997; Cannat Spinel compositions from spinel peridotites in Krivaja–Konjuh clus- et al. ,1997) show changes in compositions on a mm scale adjacent to ter at the low Cr#, high Mg# end of the range of abyssal peridotites thin gabbro veins. While gabbro veins with a range of thicknesses do (Dick and Bullen, 1984; Arai, 1994) and spinel peridotites more gener- occur in the plagioclase and transitional peridotites (Fig. 4b, c), the anal- ally (Arai et al., 2011; Barnes and Roeder, 2001). In contrast, plagioclase yses shown in Figs. 7 and 8 with high TiO2 content in cpx and spinel do peridotites have significantly higher Cr and lower Mg numbers, creating not originate near or include distinct gabbro veins, but come from sam- a gap in compositions between spinel and plagioclase peridotites ples with plagioclase patches. As described above, variations in TiO2 (Fig. 8). Abyssal peridotites have a continuum of compositions to Cr# contents were introduced by distributed, grain scale melt infiltration; up to 0.6, reflecting increasing depletion due to melt extraction (e.g. the Cr# was buffered by originally fertile spinel and plagioclase during

Hellebrand et al., 2001). The TiO2 content of abyssal spinel peridotites this process. From cross-cutting relationships we infer that the is restricted to below 0.2%, while Krivaja–Konjuh transitional and pla- gabbroveins in Krivaja represent later episodes of melt migration. gioclase peridotites have TiO2 contents up to 1% at essentially constant Examples are shown in Fig. 4c where relatively coarser-grained gabbro Cr# around 0.5, due to buffering of the latter by plagioclase (Chalot- veins overprint the earlier distributed, interstitial plagioclase patches, Prat et al., 2013). The gap in Cr and Mg number together with the ele- and in Fig. 4d where a thin gabbro vein located to the left of the hammer vated TiO2 contents implies that the composition of the transitional crosses the patchy plagioclase-rich areas at an angle. and plagioclase peridotites from Krivaja–Konjuh can not be due to pro- Replacement of opx by olivine and cpx (Fig. 6b, d) indicates that the gressive depletion by melt extraction. infiltrating melt was opx-undersaturated. This contrasts with Lanzo Outcrop scale plagioclase patches and accumulations such as where opx replaced olivine (Kaczmarek and Müntener, 2008,their those in Fig. 4d and thin section scale plagioclase patches (Fig. 6)cor- Fig. 7), and opx is observed at the contact between plagioclase mantling relate with high TiO2 contents of both cpx and spinel (Figs. 7, 8). Sim- spinel and olivine (Piccardo et al., 2007, Plate IIE). Opx saturated melts ilar combinations of plagioclase patches and high TiO2 have been were also inferred for Othris (Dijkstra et al., 2003) and the Atlantis described for example from the Ligurian and Corsican peridotites Massif (Suhr et al., 2008). Opx undersaturation likely indicates a deeper (Rampone et al., 1993, 1997), Lanzo (Kaczmarek and Müntener, origin of the melt (Jacques and Green, 1980; Kelemen, 1990), or a garnet 2008; Piccardo et al., 2007) and abyssal peridotites (Dick, 1989; pyroxenite source (Hirschmann et al., 2003). The latter has also been in- Dick and Bullen, 1984; Hellebrand et al., 2002b; Rampone et al., voked for Ti-rich melts, although low degrees of melting of a fertile 1997; Seyler and Bonatti, 1997; Tartarotti et al., 2002). These authors source may be sufficient (Davis et al., 2011). Deformation in the spinel interpret the plagioclase patches as remnants of interstitially migrat- peridotite field followed by infiltration of melt with a deeper origin ing melt. Spinel mantled by plagioclase observed in some locations has also been inferred for the Ligurides (Piccardo and Vissers, 2007). (e.g. Fig. 6b) is found only in conjunction with interstitial plagioclase In some locations coarse spinel grains in pyroxenite veins patches, suggesting the involvement of melt to enable the reaction (e.g. Fig. 4b) in the plagioclase peridotites are mantled by plagioclase. (Piccardo et al., 2007). We therefore conclude that the plagioclase However, pyroxenite veins in the spinel peridotites do not show signs of peridotites in the Krivaja–Konjuh massif are the result of melt incipient melting either at the outcrop or thin-section scale (cpx in a py- impregnation. roxenite vein analyzed in sample Tri6a is the most fertile in the massif Grain-scale melt migration and plagioclase crystallization intro- (Fig. 7)). Microstructural observations also suggest that the pyroxenite duced chemical heterogeneity at the thin-section scale. In the areas af- veins experienced the same deformation as the peridotites, in contrast fected by infiltrating melt Al2O3 in cpx and spinel is not or only to the lack of signs of deformation of plagioclase. This indicates that partially equilibrated with plagioclase. This produced populations with the pyroxenites within the massif predate melt infiltration and are not high and low Al2O3 contents at a range of TiO2 in cpx (the parallel trends the source of the intergranular melt in the plagioclase peridotites. This

2+ Fig. 8. Spinel compositions (a) Cr# (=Cr/Cr + Al) vs TiO2 and (b) Cr# vs Mg# (=Mg/Mg + Fe ). For samples termed transitional relatively depleted (Cr# of 0.4 and above) large darker brown spinels and fine-grained light brown spinels (Cr# 0.1–0.2) occur in close proximity in the same thin section, similar to cpx Al2O3 variability. In (a) a similarly broad range in TiO2 contents at fixed Cr# in harzburgites and dunites from the Hess Deep have been interpreted to indicate migrating melt (Dick and Bullen, 1984; Kelemen et al., 1997). The refertilized lherzolites from Lherz do not show elevated TiO2 contents, in contrast to the plagioclase peridotites from Ronda. Spinels from massifs with supra-subduction affinity (Mirdita) and the chromitites have similar high Cr#. In (b) the data form a continuous trend, with plagioclase peridotites from KK having the highest spinel Fe contents. Noticeably off this trend are the xenoliths with higher Mg# for a given Cr#, as well as the chromitites and rocks with supra-subduction affinity. Data sources as for Fig. 7. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) U.H. Faul et al. / Lithos 202–203 (2014) 283–299 293 is also consistent with the inference that the massif did not experience exhumation from within the garnet stability field would take of order uniform heating as a whole, as the pyroxenites are expected to melt at a of 10 Ma. With the grain growth rates for dry, melt-free olivine deter- somewhat lower temperature relative to the peridotites (Hirschmann mined by Faul and Jackson (2007), at a temperature of 950 °C grains et al., 2003). would grow to less than 250 μm in size during that time. Actual growth Among the most fertile rocks from the Krivaja–Konjuh massif are would be less since growth rates would decrease with temperature the spinel peridotites in the south and west of Krivaja that show no decreasing during uplift. This indicates that mylonitic grain sizes can signs of recrystallization or high TiO2 contents associated with melt im- be maintained during exhumation from significant depth, provided pregnation. This contrasts with Lanzo, Ronda and Lherz, where that temperatures remain relatively low. the infiltrating melt refertilized the host rock (see e.g. the cpx Al2O3 con- The transitional and plagioclase peridotites associated with melt tents for Lherz in Fig. 7). This process of refertilization, accompanied by infiltration are characterized by recovery and grain growth. This is due textural changes and grain growth, is described as ‘asthenospherisation’ to the higher temperatures indicated by opx thermometry (Table 1), (e.g.Le Roux et al., 2008; Soustelle et al., 2009; Van der Wal and Vissers, as well as enhancement of grain growth due to the presence of melt 1996). In Krivaja–Konjuh the infiltrating melt enabled grain growth and (Faul and Scott, 2006). Grain growth overprints the earlier deformation precipitation of plagioclase, but led to significant compositional changes evident in the spinel peridotites but does not completely erase it. Evi- only where relatively high volumes of melt were involved, producing dence for prior deformation includes dismembered and elongate olivine olivine-rich troctolites. grains in plagioclase peridotites that are similar to those found in spinel Evidence for continued melting at depth after the onset of rifting are peridotites (compare Figs. 5dand6b), supported by the similarity more evolved melt compositions that range from olivine gabbros to of compositions in the transitional and spinel peridotites (Figs. 7, 8). In gabbros, intruding into peridotite, forming large dikes or more massive the most uniformly coarse-grained dunites and olivine-rich troctolites outcrops. Further analysis of these rocks is needed to examine whether prior deformation is more difficult to ascertain at the thin section scale they are related to the melt that infiltrated the peridotites by porous due to grain growth facilitated by higher infiltrated melt contents. flow. Late-stage, more evolved, relatively thin gabbro veins frequently Importantly, the microstructural features due to melt infiltration in cross-cut earlier dikes and veins. These later cross-cutting veins have the peridotites, such as plagioclase patches and spinel grains mantled sharp contact (Fig. 4), implying cooling of the peridotites from condi- by plagioclase, as well as the microstructures of the olivine-rich tions when the earliest gabbro veins were formed. The peridotites troctolites as a whole, show no signs of deformation. Similarly, while therefore resided over a region of melt production at depth for some some massive gabbros show evidence for deformation, thin gabbro time. veins in peridotites appear undeformed (Fig. 4). This implies that deformation of the peridotites essentially ceased with melt infiltration, and 5.3. Peridotite temperature estimates that processes following melt infiltration, like obduction onto the metamorphic sole during closing of the ocean basin and subsequent em- Porphyroclastic opx grains are not obviously zoned but are composi- placement, did not pervasively deform the massif as a whole. tionally heterogeneous due to exsolution lamellae, recrystallization (Fig. 5a, c) and patchy replacement by olivine and cpx (Fig. 6b, d). Due 5.5. Pressure of origin to their large size they typically are not equilibrated with smaller (recrystallized) cpx grains, which themselves can have a range of com- A significant feature of the clinopyroxene compositions is that the positions in one thin section. Two-pyroxene thermometry is therefore fertile spinel peridotites from Krivaja have Na2O contents approaching not useful for estimating temperatures. Temperatures calculated from primitive upper mantle values (McDonough and Sun, 1995). The high average opx compositions for each area with the Ca-in-opx thermome- cpx Na2O contents are similar to other orogenic peridotites such as ter of (Brey and Köhler, 1990) are highest for plagioclase peridotites Ronda (Obata, 1980), Beni Bousera (Gysi et al., 2011), Lherz (Le Roux showing evidence of melt migration (up to 1200 °C), and lowest for et al., 2007), and the Eastern Central Alpine peridotites (Müntener spinel peridotites (~900 °C) that show no sign of recovery from defor- et al., 2010). High Na2O contents have been described as characteristic mation (Table 1). Similar temperatures for plagioclase and spinel peri- for subcontinental peridotites (Kornprobst et al., 1981; Seyler and dotites are also obtained for Lanzo, where the plagioclase peridotites Bonatti, 1994;seealsoBazylev et al., 2009), but the lower Na2O are also inferred to originate by melt infiltration (Kaczmarek and contents in abyssal peridotites were ascribed to greater depletion of Müntener, 2008). the latter or metasomatic enrichment of the former.

Counter to the depletion argument is the observation that Al2O3 con- 5.4. Deformation tents of cpx in fertile abyssal and orogenic peridotites are essentially the

same, but the Na2O contents in orogenic peridotites are up to twice that Highly deformed spinel lherzolites occur in the southern parts of of abyssal peridotites (Fig. 7b). The cpx compositions of harzburgites

Krivaja (Duboštica, Voj8, Fig. 5a, b); similarly deformed plagioclase from Lherz underscore that the difference in Na2O between abyssal lherzolites occur just to the north of the troctolites (Saj5). Rift-related and orogenic peridotites is not primarily a function of depletion: distal deformation of the spinel lherzolites resulted in grain size reduction to harzburgites not affected by the inﬁltrating melt that produced the mylonites and locally ultramylonites, where no porphyroclastic phase lherzolites (Le Roux et al., 2007; personal communication, 2014) have remains. With the piezometer for dry olivine of Van der Wal et al. cpx Na2O contents similar to the most fertile abyssal spinel lherzolites (1993), the smallest recrystallized grain sizes of 0.1 to 0.3 mm imply (up to 1%). Harzburgites close to the refertilized lherzolites and the stresses N20 MPa. This is signiﬁcantly higher than stresses inferred for lherzolites themselves contain twice this amount due to diffusive asthenospheric upper mantle of between 0.1 and 1 MPa (e.g. Behn refertilization by Na2O ahead of the main front. Similarly, high Na2O et al., 2009), but much lower than stress estimates for low temperature contents in cpx from the Lena Trough were ascribed to a high- ultramylonitic shear zones for example at oceanic fracture zones pressure, sub-continental origin of these rocks (Hellebrand and Snow, (Warren and Hirth, 2006)orinOman(Linckens et al., 2011). 2003).

The lack of recovery of the spinel lherzolites implies temperatures The pressure dependence of clinopyroxene Na2O contents has also well below the solidus during uplift and exhumation, consistent with been investigated experimentally. The experiments show that the temperature estimates from opx thermometry (Table 1). Exhumation Na2O contents increase with increasing pressure. At ﬁxed starting com- rates on detachment faults along the Mid-Atlantic Ridge are observed position Na2O increases from below ~1 wt.% at 1–1.5 GPa to 2 wt.% at to be of order of the full spreading rate of 3 cm/year (Grimes et al., 3 GPa, before leveling off with further pressure increase (Putirka et al., 2008). Assuming a rate of 1 cm/year for the Krivaja–Konjuh massif, 1996; Tuff et al., 2005, see also Blundy et al., 1995). The experimental 294 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

observations suggest therefore that the high Na2O contents of the oro- above, the high cpx Na2O contents indicate a subcontinental origin of genic peridotites are due to their higher pressure origin relative to abys- parts of Krivaja. In contrast, the spinel peridotites in Konjuh have signif- sal peridotites. A high pressure origin for the orogenic peridotites is icantly lower cpx Na2O contents. Comparison with cpx compositions supported by the occurrence of garnet pyroxenites in these massifs. Ad- from spinel peridotites from the Gakkel ridge, described as covering ditionally, modeling by Müntener et al. (2010) shows that Na-rich but the range of global compositions (Hellebrand et al., 2005), and those Nd-poor cpx compositions of the Alpine peridotites indicate melting from the Southwest Indian Ridge, tending towards more enriched com- in the garnet stability ﬁeld. positions (Seyler et al., 2003), shows that they have Al2O3 contents Independent indications of a relatively high pressure origin of the as high to those from Krivaja–Konjuh and other orogenic peridotites. spinel peridotites from Krivaja come from microstructural observations. However, their TiO2 contents are restricted to below 0.4 wt.%, similar While no garnet has yet been observed in the pyroxenites, garnet- to peridotites from Konjuh and a massif inferred to represent oceanic shaped symplectites (Fig. 5f) and coarse opx-spinel symplectites in pe- lithosphere (Monte del Estados, Puerto Rico, Marchesi et al., 2011). Spi- ridotites (Fig. 5e) occur in a number of locations (Tajašnica, Duboštica, nel peridotites from orogenic massifs such as Lherz (Le Roux et al., Sajavica). The orthopyroxene in the symplectite in Fig. 5eshowsexsolu- 2007), Ronda (Obata, 1980) and the Alps (Müntener et al., 2010)over- tion lamellae, like other opx porphyroclasts. In Lanzo and Mt. Maggiore lap the compositional range of TiO2 and Al2O3 in cpx of Krivaja, but only (Corsica) ﬁner scale symplectites, consisting of spinel plus opx without the Alpine plagioclase peridotites extend to similarly high TiO2 contents. exsolution lamellae, occur within opx porphyroclasts near their grain Spinel TiO2 contents in Konjuh are also lower than Krivaja. boundaries. The latter are interpreted as being due to exsolution of Al Spinel peridotites from Krivaja–Konjuh do not range to the depleted from opx during cooling (Piccardo et al., 2007; Rampone et al., 2008). end of abyssal harzburgites with cpx Al2O3 contents as low as 2% and The coarse symplectites, representing individual grains, are interpreted TiO2 contents below 0.1% (e.g. from the Mid-Atlantic Ridge, Seyler as originating from breakdown of garnet at spinel-facies conditions. et al., 2007,HessDeep,Arai and Matsukage, 1996, Fig. 7). The depleted

From the combination of microstructural observations and Na2O-rich abyssal peridotite compositions overlap with the Eastern Mirdita cpx we infer a relatively high pressure, subcontinental origin for the spi- ophiolite which is inferred to originate in a supra-subduction setting nel peridotites found in the Krivaja. Na2O contents below DMM for the (Dilek, 2003; Morishita et al., 2011). fertile spinel peridotites from Konjuh with similar cpx Al2O3 contents in- The signiﬁcance of the shear zone between the Krivaja and Konjuh dicate a lower pressure origin, similar to fertile abyssal peridotites. portions is not obvious, as some of the more depleted south-eastern

parts of Krivaja (Vojnica and Tribija) are also lacking the TiO2 and 5.6. Traces of subduction Na2O enrichment, similar to Konjuh. Other indicators of fertility such as cpx Al2O3 contents, olivine Mg# and spinel Cr# and Mg# cover the The compositions of the chromitites near Duboštica (see Fig. 2 and same range in both parts. Konjuh also appears not to have experienced Table 1) are distinct from all other compositions found in the massif the same high degree of deformation as the fertile spinel peridotites (Figs. 7, 8). Their Cr# are similar to harzburgites and dunites from the from Krivaja. The latter locally have no porphyroclasts remaining, Eastern Mirdita ophiolite, which has supra-subduction affinity (Dilek, but the fertile spinel peridotites from Konjuh show only partial recrys- 2003; Dilek et al., 2005; Morishita et al., 2011), but the Krivaja tallization of olivine, with pyroxene affected by deformation but not re- chromitites have somewhat higher Mg# and TiO2 contents. Composi- crystallized. Overall the compositional characteristics of Krivaja indicate tions in the Krivaja–Konjuh massif are too fertile to produce melts that a subcontinental origin, while those of Konjuh suggest an suboceanic would be in equilibrium with the Cr# found in the chromitites (Arai, origin. However, both parts are similar in their fertility. 1994; Arai et al., 2011). Barnes and Roeder (2001) note that boninites are the only group of magmas that commonly contain spinels that are 6. Relationship to the Balkan peridotite massifs as Cr-rich as those typical of ophiolitic chromitites. Due to the low solu- bility of Cr-spinel in silicate melts chromitites require melt-rock ratios of For the tectonic context it is useful to clarify the names of the respec- more than 300 to form (Kelemen et al., 1997). The absence of significant tive units found in the literature. The Dinaride Ophiolite belt and Vardar outcrops of dunite in the Krivaja, with which chromitites are usually as- Zone Western Belt as described here (Bazylev et al., 2009; Karamata, sociated, also indicates that the melt that produced the chromitites is 2006; Pamić et al., 2002) are collectively referred to as the Western not derived from the massif itself. Vardar Ophiolitic Unit by Schmid et al. (2008) to distinguish it from Since the chromitites appear to be unrelated to the massif we infer the ophiolites of the Eastern Vardar Ophiolitic Unit (or Main Vardar that they represent a later episode of melt migration. The metamorphic Belt, Karamata, 2006), separated from the Western Unit by the Sava sole indicates that the massif was thrust onto oceanic crust, prior to Zone. The following refers only to the Western Vardar Ophiolitic Unit obduction and inclusion in the mélange. The composition of the (i.e. Dinarides and Vardar Zone Western Belt). chromitites suggests a subduction-related origin, indicating that the Differences in the petrology and geochemistry between the Dinaride massif was the upper plate during closure of the ocean basin. Depleted and Vardar zone belts (e.g. Lugović et al., 1991) have been used to infer and hydrous melts from the mantle wedge below traversed the Krivaja that the two belts originated in different ocean basins (e.g. Dilek et al., peridotites in localized conduits. Their fertile compositions imparted a 2008; Karamata, 2006; Pamić et al., 2002; Robertson and Karamata, higher spinel Mg# and cpx TiO2 content in comparison to most 1994 and references therein). In contrast, some authors have invoked chromitites (Barnes and Roeder, 2001), although temperature can also a single ocean model for the origin of both belts (e.g. Schmid et al., affect spinel Mg# (Arai et al., 2011). These localized melt conduits may 2008; Smith and Spray, 1984). In light of these different models we be related to basaltic dikes in the south-eastern part of the massif that compare compositions from the Krivaja–Konjuh massif from this have suprasubduction major and trace element affinity (Lugović et al., study to compositions from other peridotite massifs from both the 2006). The important implication is that particularly in the western Dinarides and the Vardar zone (Bazylev et al., 2009), as well as the Dinarides volcanics with supra-subduction affinity are unlikely to be re- Mirdita ophiolite in Albania from Morishita et al. (2011). lated to the peridotites that have fertile, subcontinental characteristics. Whole rock analyses were performed by Lugović et al. (1991) for Krivaja–Konjuh and by Bazylev et al. (2009) for a number of massifs 5.7. Summary of the compositional characteristics of Krivaja and Konjuh within the Dinarides and Vardar zone. Fig. 9 shows anhydrous

whole rock compositions for the oxides Al2O3 and TiO2, considered Comparison of the compositions of the two parts of the massif with least affected by alteration. The compositions of the Krivaja–Konjuh each other and with peridotites from different tectonic settings places spinel lherzolites (Lugović et al., 1991) and the western massifs of the constraints on the likely origin of rocks from the massif. As discussed Dinarides (Bazylev et al., 2009) (see Fig. 1) are comparable to the U.H. Faul et al. / Lithos 202–203 (2014) 283–299 295

N 1.6 wt.%) it is grouped here with the eastern massifs of the

Dinarides, rather than the Vardar zone (cpx Al2O3 b 3wt.%,bulk rock b 1%). Below 0.25 wt.% Na2OtheAl2O3 content drops quickly, but rocks from the Vardar Zone still have consistently higher values compared to Mirdita, Tuzinje and Brezovica. The same groups are also identiﬁable in the spinel compositions (Fig. 10b). The Dinarides include compositions that coincide with the fertile end of abyssal peridotites (Fig. 8), (e.g. Dick and Bullen, 1984), while rocks from the Vardar zone range to compositions that overlap with arc harzburgites (Arai, 1994; Ishii et al., 1992). The plagioclase peridotites from Krivaja–Konjuh and the western massifs of the Dinarides

diverge from the depletion trend to elevated TiO2 contents. The western massifs therefore are characterized by melt inﬁltration, possibly at the Fig. 9. Select anhydrous whole rock compositions from orogenic massifs (Bodinier et al., onset of rifting, while the eastern massifs and the Vardar zone either 1988; Frey et al., 1985; Le Roux et al., 2007), an oceanic massif (Monte del Estado, Marchesi et al., 2011) and abyssal peridotites (Casey, 1997) compared to compositions from the show only the effects of depletion, or migrating melts were of a different Krivaja–Konjuh massif itepLu91 and the Dinarides and Vardar Zone (Bazylev et al., character, not enriched in TiO2. 2009). DMM from Workman and Hart (2005). The compositions from the western Overall the clinopyroxene compositions of the Balkan peridotite Dinarides overlap with orogenic massifs, while the eastern Dinarides are more similar to massifs show a decrease in Na2O from west to east, indicating decreas- compositions from a relatively fertile oceanic massif. ing pressures of equilibration. Fertility also decreases systematically as shown by mineral and bulk rock compositions (Figs. 9 and 10). This sug- relatively fertile compositions of other orogenic massifs such as Lherz gests a gradual progression in tectonic setting from subcontinental on (Le Roux et al., 2007), Ronda (Frey et al., 1985) and Lanzo (Bodinier the western edge of the Dinarides, to fertile abyssal peridotite composi- et al., 1988). The eastern massifs of the Dinarides are somewhat less tions of Konjuh to somewhat more depleted compositions of the eastern fertile, comparable to compositions from the Monte del Estado massif, massifs. Compositions of the Vardar Zone massifs are at the depleted described as originating from oceanic lithosphere (Marchesi et al., end of abyssal peridotites, possibly transitioning to supra-subduction af- 2011). At the more depleted end rocks from the Vardar zone are similar ﬁnity. Grouping the Banjska massif with the eastern Dinarides due to to depleted abyssal peridotites (Casey, 1997). their similar fertility forms a continuous structural trend of parallel

Clinopyroxene Na2OvsAl2O3 separates different groups of mas- bands from south of the Alps to the Hellenides (Fig. 1). The gradual sifs (Fig. 10a). To exclude the effects of plagioclase crystallization change in compositions from west to east is consistent with the ‘single on clinopyroxene compositions only spinel peridotites are plotted. ocean’ hypothesis of the peridotite massifs of the Dinarides and Vardar Fig. 10 shows that compositions from Krivaja–Konjuh cover the zone of Schmid et al. (2008) with a fertile western continental margin same range as the western massifs of the Dinaride ophiolite belt and a depleted, possibly subduction inﬂuenced margin on the eastern (Borja, Ljubić–Čavka, Bistrica, Sjenički Ozren; see Fig. 1). The effect side. of pressure on cpx Na2O content is emphasized by the fact that In contrast to the gradual change from west to east, there is a distinct Al2O3 only decreases moderately for a range of Na2Ofrom2to break in compositions at the southern end of the Dinarides. While 1 wt.%, with fertile rocks from Konjuh at the low end of the range. Sjenički Ozren shows subcontinental afﬁnity, the Eastern Mirdita and The massifs on the eastern side of the Dinarides (Bosanski Ozren, Brezovica massifs have been linked to a supra-subduction setting

Zlatiborand Banjska), show decreasing Al2O3 contents at Na2O (Bazylev et al., 2003; Dilek et al., 2008; Morishita et al., 2011). A distinct below 1 wt.%. The Banjska massif is usually considered part of the drop in fertility occurs over a distance of only about 20 km between

Vardar zone, but due to its fertility (cpx Al2O3 N 4wt.%,bulkrock Sjenički Ozren with Al2O3 between 4–7% and the Tuzinje massif with

Fig. 10. Peridotite compositions from Krivaja–Konjuh (this study, Šegvić,2010), the Dinarides and Vardar zone (Bazylev et al., 2009), as well as the Mirdita ophiolite in Albania (Morishita et al., 2011). Symbol colors correspond to colors in Fig. 1. (a) Cpx Al2O3 vs Na2O for spinel peridotites only. Data from the pyroxenite in Tri6a are not shown. Overall the data form a continuous trend with Al2O3 contents only deceasing substantially below 0.5 wt.% Na2O. The western Dinarides are the most fertile, while the massifs on the eastern side (Zlatibor and Bosanski Ozren) are more depleted, overlapping with Vardar zone compositions. Compositions from Brezovica and Tuzinje in the south overlap with the Eastern Mirdita ophiolite with supra-subduction affinity (Dilek, 2003; Dilek et al., 2008; Morishita et al., 2011). (b) Spinel Cr# vs TiO2 content. As for clinopyroxene the spinel compositions show progressive depletion from west to east. The plagioclase peridotites deviate from this trend at Cr# between 0.4 and 0.6 due to the effects of melt migration (see text). The Brezovica and Tuzinje spinels have the highest Cr#, along with the chromitites from the southern part of Krivaja, similar to compositions from Eastern Mirdita. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 296 U.H. Faul et al. / Lithos 202–203 (2014) 283–299 less than 2%. A similar contrast in fertility exists between the Banjska described below, the peridotites record earlier processes related to the massif and the massifs to the south. opening of the ocean basin. The Peć-Srbica line (or Scutari-Peć lineament) is inferred to The earliest record in the massif is the deformation of the spinel represent a structural break between the Dinarides and Hellenides lherzolites (Fig. 11a). Significant strain is indicated by the degree of re- (e.g. Smith, 1993) and has been interpreted as a transform fault crystallization, locally to ultramylonites. Based on the calculated tem- between a rift basin to the northwest and a small ocean basin to the perature, lack of recovery and high cpx Na2O contents of these rocks southeast (Robertson et al., 2009). Dilek et al., (2005), citing the com- the deformation took place at relatively high pressures and lithospheric plete ophiolitic sequence of the Western Mirdita massif with extensive temperatures, representing lithospheric thinning at the onset of rifting. volcanics just to the south of the line, argue that this productivity is in- Continued thinning of the lithosphere resulted in upwelling of astheno- compatible with a fracture zone, and that it belonged to a spreading sphere and onset of melting at depth, producing opx-undersaturated center. A further complication is that the Tuzinje massif is composition- melts. On upward migration this melt infiltrated portions of the thinned ally more similar to the depleted massifs to the south (Bazylev et al., lithosphere, heating it (Fig. 11b). This resulted in partial conversion of 2009), but lies to the north of this line. spinel to plagioclase and the onset of recovery and grain growth seen in the transitional and plagioclase peridotites. Melt impregnation overprinted but did not erase the texture originating with lithospheric 7. Evolution of the Krivaja–Konjuh Massif extension. The fault structures in the massif suggest exhumation of the peri- The structural and petrological observations detailed above can be dotites along localized shear zones without further pervasive defor- placed in the context of the tectonic evolution of the Balkans discussed mation (Fig. 11c). The relatively low volumes of melt produced at in a range of publications. A number of the observations and inferences depth froze in the thermal boundary layer either as interstitial melt need to be further substantiated, the following is intended to provide a in plagioclase peridotites, troctolites or gabbro intrusions. This lead framework for this. The ophiolites of the Dinarides and Vardar zone to exposure of peridotites at the seafloor without volcanic cover, pro- are inferred to be at least of early Triassic age, originating in a Tethys- ducing ophicalcites. associated ocean (e.g. Pamić et al., 2002). Rift related igneous and Progressive thinning resulted in melting to shallower depth with sedimentary rocks are of late Permian age, while radiolarian cherts asso- overall higher melt production and consequent greater depletion of ciated with MOR type basalts are dated as late Triassic (Robertson et al., the peridotites, recorded in the eastern Dinarides (Fig. 11d). Continued 2009). Agreed upon dates exist only for the metamorphic sole of spreading then migrated eastwards towards the Vardar zone. In this the Krivaja–Konjuh massif, with ages ranging from 174–157 Myr. As scenario the Krivaja would represent the western margin of the

c d

Fig. 11. Evolution of the Krivaja–Konjuh massif and the Dinarides and Vardar zone. The model follows those proposed for example by Pamić et al. (2002) and Robertson et al. (2009),but accounts for specific events identifiable in the peridotites of the Krivaja–Konjuh massif. (a) Onset of lithospheric thinning. Pervasive deformation, at lithospheric temperatures and pressures near the spinel garnet transition. Possible onset of localization. (b) Onset of melting in upwelling asthenosphere and infiltration of the melt into the thinned lithosphere. Melt infiltration raises the temperature, enabling reaction to plagioclase and recrystallization. Melt impregnation overprints but does not erase pre-existing texture. Deformation further localizes in shear zones. (c) Creation of an ocean basin due to continued extension. Exhumation of peridotites to the ocean floor. Continued melting and migration of deeper melt converts some plagioclase peridotites to troctolites. Intrusion of massive gabbros accommodates extension without further pervasive deformation. (d) Evolution of the spreading center to a mid-ocean ridge. Melting to shallower depth leads to increasing depletion of peridotites, forming the Eastern Dinarides and possibly Vardar zone peridotites. (e) Subduction and beginning of closure of the ocean basin. Dinarides are part of the overriding plate locally traversed by mantle-wedge derived melts, forming the chromitites and other supra-subduction related volcanics in the Krivaja–Konjuh massif and Dinarides. Vardar zone may be a backarc spreading center. (f) Closure of the ocean basin pushes Dinarides onto subducting slab, creating the metamorphic sole. Continued shortening leads to obduction and incorporation into the melange. U.H. Faul et al. / Lithos 202–203 (2014) 283–299 297

Meliata–Maliac Ocean, separated from the Neotethys to the east by a depleted relative to the Dinarides and are associated with a supra- spreading ridge in the Late Triassic (Schmid et al., 2008). subduction setting, appears to be localized rather than gradual. The next distinct record is the chromitites in the south of Krivaja, interpreted as localized conduits for subduction related melts. This Acknowledgements implies that the Krivaja was the overriding plate above a subducting slab (Fig. 11e). Progressive subduction formed the approximately Reviews of an earlier version by Carlos Garrido and Shoji Arai and – west east aligned series of chromitites (Federal Geological Institute, by two anonymous reviewers improved the manuscript. The help of – 1971 1990), as well as other supra-subduction-related volcanics, Neel Chatterjee and Bob Rapp with microprobe analyses is gratefully which are not considered to be co-magmatic with the peridotites acknowledged. This work was partially supported by NSF grant EAR (Bazylev et al., 2009). Depleted rocks such as harzburgites and dunites 0838447 to UF. in otherwise relatively fertile massifs of the Dinarides may similarly represent localized suprasubduction-related melt migration. This is sug- Appendix A. Supplementary data gested by the flat or spoon-shaped cpx trace element patterns of harzburgites and dunites from Bistrica and Zlatibor that contrast with Supplementary data to this article can be found online at http://dx. the more LREE depleted, but significantly higher M-HREE patterns doi.org/10.1016/j.lithos.2014.05.026. of the lherzolites from these massifs (Bazylev et al., 2009). While the latter are interpreted to reflect low degrees of partial melting, the former are associated with chromatographic effects or advective References melt transport (Hellebrand et al., 2002a). By comparison, cpx from the Arai, S., 1994. Characterization of spinel peridotites by olivine–spinel compositional rela- suprasubduction-related Brezovica massif have U-shaped patterns tionships: review and interpretation. Chemical Geology 113, 191–204. with significantly enriched LREE. Arai, S., Matsukage, K., 1996. Petrology of the gabbro–troctolite–peridotite complex, Hess Intra-oceanic subduction closed the ocean basin during the Jurassic, Deep, equatorial Pacific: implications for mantle–melt interactions within the oceanic lithosphere. In: Mével, C., Gillis, K.M., Allan, J.F., Meyer, P.S. (Eds.), Proc. Ocean Drill. generating the metamorphic sole (Fig. 11f). On closure of the ocean Program, Scientific Results, Vol. 147. ODP, College Station, Tx, pp. 135–155. basin, the massif, including the metamorphic sole, was obducted onto Arai, S., Okamura, H., Kadoshima, K., Tanaka, C., Suzuki, K., Ishimaru, S., 2011. Chemical the Adriatic plate and thrust onto the Triassic and Jurassic limestones characteristics of chromian spinel in plutonic rocks: implications for deep magma – in the ophiolitic mélange. Diapiric emplacement of the massif as a processes and discrimination of tectonic setting. Island Arc 20, 125 137. Armstrong, J.T., 1995. CITZAF—a package for correction programs for the quantitative whole in its current position within the mélange is precluded by the electron microbeam X-ray analysis of thick polished materials, thin-films and parti- low temperature conditions during emplacement indicated by the con- cles. Microbeam Analysis 4, 177–200. fi tact of peridotite with the underlying limestone. As indicated above, the Barnes, S.J., Roeder, P.L., 2001. The range in spinel compositions in terrestrial ma cand ultramafic rocks. Journal of Petrology 42, 2279–2302. southern end of the Dinarides at the transition to the Albanian Bazylev, B.A., Karamata, S., Zakariadze, G.S., 2003. Petrology and evolution of the ophiolites has a different, supra-subduction related character, indicating Brezovica ultramafic massif, Serbia. Geological Society, London, Special Publications a somewhat different origin. 218, 91–108. http://dx.doi.org/10.1144/GSL.SP.2003.218.01.06 (91-108). Bazylev, B.A., Popević, A., Karamata, S., Kononkova, N., Simakin, S., Olujić, J., Vujnović,L., Memović, E., 2009. Mantle peridotites from the Dinaridic ophiolite belt and the Var- 8. Conclusions dar zone western belt, central Balkan: a petrological comparison. Lithos 108, 37–71. http://dx.doi.org/10.1016/j.lithos.2008.09.011. – Behn, M.D., Hirth II, G., J. R. E., 2009. Implications of grain size evolution on the seismic The peridotites of the Krivaja Konjuh massif record a complex histo- structure of the oceanic upper mantle. Earth and Planetary Science Letters 282, ry that ranges from early rifting to traces of subduction. In the Krivaja 178–189. http://dx.doi.org/10.1016/j.epsl.2009.03.014. fertile peridotites of relatively high pressure origin are pervasively Blundy, J.D., Falloon, T.J., Wood, B.J., Dalton, J.A., 1995. Sodium partitioning between clinopyroxene and silicate melts. Journal of Geophysical Research 100, 15,501–15,515. deformed at lithospheric temperatures, likely recording rifting of sub- Bodinier, J.-L., Dupuy, C., Dostal, J., 1988. Geochemistry and petrogenesis of Eastern continental lithosphere. Some of these rocks are subsequently infiltrat- Pyrenean peridotites. Geochimica et Cosmochimica Acta 52, 2893–2907. ed by a melt of deeper origin, causing changes in the mineral modes and Brey,G.P.,Köhler,T.,1990.Geothermobarometry in four-phase lherzolites II. New assemblage (dissolution of opx and precipitation of plagioclase), as well thermobarometers, and practical assessment of existing thermobarometers. Journal of Petrology 31, 1353–1378. as recovery and grain growth. The rocks affected by melt infiltration Cannat, M., 1993. Emplacement of mantle rocks in the sea-floor at mid-ocean ridges. show no further deformation. The most fertile portions of Konjuh Journal of Geophysical Research 98, 4163–4172. are similar in composition to the fertile portions of Krivaja, but do not Cannat, M., Chatin, F., Whitechurch, H., Ceuleneer, G., 1997. Gabbroic rocks trapped in the upper mantle at the Mid-Atlantic Ridge. In: Karson, J.A., Cannat, M., Miller, D.J., Elton, show the high pressure signature and are not as highly deformed. D. (Eds.), Proceedings of the Ocean Drilling Program, Scientific Results, vol. 153. Plagioclase peridotites have the same textural characteristics indicating Ocean Drilling Program, College Station, TX, pp. 243–264. Casey, J.F., 1997. Comparison of major and trace-element geochemistry of abyssal perido- melt infiltration as in Krivaja, but are not as enriched in TiO2.Harzburgites tites and mafic plutonics with basalts from the MARK region of the Mid-Atlantic and dunites are essentially absent, but large areas of olivine-rich ridge. In: Karson, J.A., Cannat, M., Miller, D.J., Elton, D. (Eds.), Proceedings of the troctolites occur in the center of Krivaja. Ocean Drilling Program, Scientific Results, vol. 153. Ocean Drilling Program, College In the southern part of Krivaja very localized migration of a much Station, TX, pp. 181–241. fi Chalot-Prat, F., Falloon, T.J., Green, D.H., Hibberson, W.O., 2013. Melting of plagioclase + more depleted melt with possible boninitic af nity is recorded by the spinel lherzolite at low pressures (0.5 GPa): an experimental approach to the occurrence of chromitites. The compositions of spinels in the chromitites evolution of basaltic melt during mantle refertilisation at shallow depths. Lithos are distinctly different and have no counterpart anywhere else within 172–173, 61–80. Davis, F.A., Hirschmann, M.M., Humayun, M., 2011. The composition of the incipient the massif, either in ultramaficormafic lithologies. The chromitites, partial melt of garnet peridotite at 3 GPa and the origin of OIB. Earth and Planetary however, maybe linked to the volcanic rocks with supra-subduction Science Letters 308, 380–390. affinity found in the vicinity of the massif. This suggests that the Dick, H.J.B., 1989. Abyssal peridotites, very slow spreading ridges and ocean ridge – chromitites were created during closing of the ocean basin, where the magmatism. Geological Society, London, Special Publications 42, 71 105. Dick, H.J.B., Bullen, T., 1984. 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Diffuse porous the Vardar zone (Fig. 1) corresponds to an ocean–continent transition melt flow and melt-rock reaction in the mantle lithosphere at a slow-spreading ridge: a structural petrology and LA-ICP-MS study of the Othris peridotite as envisioned for remnants of the Alpine Tethys. In contrast, the transi- massif (Greece). Geochemistry, Geophysics, Geosystems 4, 8613. http://dx.doi.org/ tion to the Albanian and Greek ophiolites, which are much more 10.1029/2001GC000278. 298 U.H. Faul et al. / Lithos 202–203 (2014) 283–299

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